US20130050289A1 - Led driver apparatus - Google Patents
Led driver apparatus Download PDFInfo
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- US20130050289A1 US20130050289A1 US13/586,296 US201213586296A US2013050289A1 US 20130050289 A1 US20130050289 A1 US 20130050289A1 US 201213586296 A US201213586296 A US 201213586296A US 2013050289 A1 US2013050289 A1 US 2013050289A1
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- led
- led array
- driver apparatus
- drivers
- array
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- 238000000034 method Methods 0.000 claims abstract description 18
- 239000004973 liquid crystal related substance Substances 0.000 claims description 7
- 230000005669 field effect Effects 0.000 claims description 3
- 230000003071 parasitic effect Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 5
- 230000010363 phase shift Effects 0.000 description 3
- 238000003491 array Methods 0.000 description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 2
- 229910052753 mercury Inorganic materials 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
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Classifications
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/3406—Control of illumination source
- G09G3/342—Control of illumination source using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/37—Converter circuits
- H05B45/3725—Switched mode power supply [SMPS]
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/0626—Adjustment of display parameters for control of overall brightness
- G09G2320/064—Adjustment of display parameters for control of overall brightness by time modulation of the brightness of the illumination source
Definitions
- the following description relates to a Light Emitting Diode (LED) driver apparatus, and to, for example, an LED driver apparatus that can supply a stable constant current to an LED array by using a plurality of constant current sources.
- LED Light Emitting Diode
- LCDs Liquid Crystal Displays
- LCDs are widely used because they are relatively thinner and light-weight in comparison to many other types of display apparatuses and exhibit lower driving voltage and consumes less power.
- the liquid crystal used in an LCD is a non-emitting substance that does not emit light by itself.
- an LCD requires an additional backlight for supplying light to its liquid crystal panel.
- CCFL Cold Cathode Fluorescent Lamp
- LED Light Emitting Diode
- CCFLs use mercury and thus may cause environmental pollution.
- CCFLs exhibit a slow response speed and a low color representation.
- CCFLs are inappropriate for making an LCD that is light-weight, thin, short, and/or small in size.
- LEDs do not use harmful materials such as mercury and are thus environment-friendly. In addition, LEDs allow impulse driving. Also, a light source made with LEDs exhibits a high color representation, with the ability to independently adjust the amount of light emitted from red (R), green (G), and blue (B) diodes to change the luminance, the color temperature, and the like of the obtained image. Thus, LEDs are appropriate for making an LCD that is light-weight, thin, short, and/or small in size. Therefore, LEDs have been widely used as a backlight source of LCDs and other display devices.
- a DC-DC converter is often used to adjust a power source supplied to the LEDs, and a driving circuit that functions as a constant current source is often used to supply a constant current to the LEDs.
- the LEDs are often driven by using the same current regardless of voltages of the LEDs.
- a single constant current source may be provided under an LED array to supply the same constant current to the LED array.
- a constant current source is typically implemented with a transistor.
- a parasitic capacitance component of the transistor may become very large. This may reduce the stability of the current and/or lengthen the settlement time of the constant current.
- a large capacitance may be required to compensate for the parasitic capacitance component, and to, for instance, maintain the stability of the system.
- the settlement time of the constant current source may lengthen, slowing down the time required to achieve a steady current.
- a Light Emitting Diode (LED) driver apparatus including: a DC-DC converter configured to supply a driving voltage to an LED array, a plurality of LED drivers configured to drive the LED array according to a dimming signal, in which the plurality of LED drivers are connected to one another in parallel to supply currents to the LED array.
- a DC-DC converter configured to supply a driving voltage to an LED array
- a plurality of LED drivers configured to drive the LED array according to a dimming signal, in which the plurality of LED drivers are connected to one another in parallel to supply currents to the LED array.
- the general aspect of LED driver apparatus may further include an input unit configured to receive the dimming signal from an external device.
- the LED drivers may be configured to supply the currents having the same amplitude to the LED array.
- the LED drivers may be configured to supply the currents having different amplitudes to the LED array.
- each of the LED drivers may include: a resistor having a first end that is grounded, a switching unit configured to selectively connect an end of the LED array to a second end of the resistor, and a comparator configured to compare a preset reference voltage with a voltage of a common node that connects to both the switching unit and the resistor.
- the switching unit may be a Field-Effect Transistor (FET) that comprises a drain connected to an end of the LED array, a source may be connected to the common node, and a gate may be connected to an output node of the comparator.
- FET Field-Effect Transistor
- the comparator may be an Operational Amplifier (Op-Amp) that is configured to receive the reference voltage through a positive terminal, to receive the voltage of the common node through a negative terminal, and to output a difference between the reference voltage and the voltage of the common node to the gate of the FET.
- Op-Amp Operational Amplifier
- the comparator may be configured to operate according to the dimming signal.
- the general aspect of the LED driver apparatus may further include: a controller configured to control an operation of the plurality of LED drivers according to an amplitude of a current required for the LED array.
- the LED array may be driven under a current having an amplitude between 50 mA and 150 mA.
- the general aspect of the LED driver apparatus may further include: a Pulse Width Modulation (PWM) signal generator configured to receive the dimming signal and generate a PWM signal, and the DC-DC converter may be configured to provide a forward bias voltage to the LED array based on the generated PWM signal.
- PWM Pulse Width Modulation
- a Liquid Crystal Display including: a liquid crystal panel, and a backlight unit comprising an LED driver apparatus of claim 1 .
- a method of driving an LED array involving: supplying a driving voltage to an LED array using a plurality of LED drivers based on a dimming signal, in which the plurality of LED drivers receive the dimming signal from an external device, the plurality of LED drivers are connected to one another in parallel to supply currents to the LED array.
- the general aspect of the method may further involve generating a Pulse Width Modulation (PWM) signal based on the dimming signal, and supplying the PWM signal to a DC-DC converter that is configured to provide a forward bias voltage to the LED array.
- PWM Pulse Width Modulation
- the LED drivers may be configured to supply the currents having the same amplitude to the LED array.
- the general aspect of the method may further involve: controlling an operation of the plurality of LED drivers according to an amplitude of a current required for the LED array as determined according to an external control or an internal calculation.
- each of the LED drivers may include: a resistor having a first end that is grounded, a switching unit configured to selectively connect an end of the LED array to a second end of the resistor, and a comparator configured to compare a preset reference voltage with a voltage of a common node that connects to both the switching unit and the resistor.
- FIG. 1 is a diagram illustrating an example of a Light Emitting Diode (LED) driver apparatus.
- LED Light Emitting Diode
- FIG. 2 is a circuit diagram illustrating examples of LED drivers.
- FIG. 3 is a circuit diagram illustrating other examples of LED drivers.
- LED Light Emitting Diode
- FIG. 1 illustrates an example of a Light Emitting Diode (LED) driver apparatus 1000 .
- LED Light Emitting Diode
- the LED driver apparatus 1000 includes an input unit 100 , a Pulse Width Modulation (PWM) signal generator 200 , a DC-DC converter 300 , an LED driver 400 , and an LED array 500 .
- PWM Pulse Width Modulation
- the input unit 100 receives a dimming signal that is used to drive the LED array 500 .
- Examples of digital dimming methods that may be used with an LED include, but are not limited to, a direct mode, a fixed phase mode, and a phase shift mode.
- a direct mode refers to a method of controlling a frequency and an On-Duty signal through a Packet Assembler/Disassembler (PAD).
- PAD Packet Assembler/Disassembler
- a fixed phase mode and a phase shift mode refer to methods of generating a PWM frequency in an Integrated Circuit (IC) and receiving only an On-Duty signal through a PAD to control the PWM frequency and the On-Duty signal.
- a dimming signal refers to a signal that is used to adjust the luminance, color temperature, and the like, of an LED or to compensate for the color temperature of the LED.
- a direct mode in which the dimming signal is received from an external device is described.
- An external device refers to a device that is outside of the LED driver apparatus 1000 .
- other modes such as the fixed phase mode and the phase shift mode, may be used to obtain the dimming signal in other examples.
- the PWM signal generator 200 generates a PWM signal that is used to adjust a power source of the LED array 500 .
- the PWM signal generator 200 generates the PWM signal that is used to control an amplitude of a driving voltage of the DC-DC converter 300 .
- the DC-DC converter 300 includes a transistor that performs a switching operation and supplies a driving voltage to the LED array 500 according to the switching operation of the transistor.
- the DC-DC converter 300 may convert a DC voltage based on the PWM signal generated by the PWM signal generator 200 and may supply the converted DC voltage, such as the driving voltage, to the LED array 500 .
- the DC-DC converter 300 may supply a voltage corresponding to a forward bias voltage of the LED array 500 to the LED array 500 so that the LED array 500 operates in a current saturation range.
- a plurality of LED drivers 400 drive the LED array 500 according to the dimming signal.
- the LED drivers 400 may adjust a driving current of the LED array 500 by using the dimming signal input from the input unit 100 .
- the LED drivers 400 may supply the same constant current or different constant currents to the LED array 500 .
- the structures and operations of the LED drivers 400 are further described later with reference to FIG. 2 .
- the controller 600 controls operations of the LED drivers 400 according to an amplitude of a constant current required for the LED array 500 .
- the controller 600 may calculate the amplitude of the constant current required for the LED array 500 according to an external control or an internal calculation and may control all or only a portion of the LED drivers 400 that are appropriate for operating under the calculated amplitude of the constant current.
- each of four LED drivers 400 may supply a constant current of a maximum of 25 mA, and a maximum amplitude of a constant current required for the LED array 500 connected to the four LED drivers is 100 mA
- the controller 600 may control all of the four LEDs 400 to operate.
- the controller 600 may control only two LED drivers 400 to operate.
- the LED driver apparatus 1000 supplies a constant current to the LED array 500 by using a plurality of LED drivers. Therefore, the LED driver apparatus 1000 may secure a stable current and a fast settlement time.
- FIG. 2 is a circuit diagram illustrating a plurality of LED drivers according to an example of LED driver apparatus 1000 .
- a plurality of LED drivers 400 - 1 , 400 - 2 . . . 400 - n are connected to one another in parallel and supply constant currents to the LED array 500 .
- the constant currents supplied from the plurality of LED drivers 400 to the LED array 500 may have the same amplitude or may have different amplitudes.
- Each of the plurality of LED drivers 400 - 1 , 400 - 2 . . . 400 - n includes switching units 410 - 1 , 410 - 2 . . . 410 - n , comparators 420 - 1 , 420 - 2 . . . 420 - n , and resistors 430 - 1 , 430 - 2 . . . 430 - n.
- the switching units 410 - 1 , 410 - 2 . . . 410 - n respectively perform switching operations according to output signals of the comparators 420 - 1 , 420 - 2 . . . 420 - n .
- the switching units 410 - 1 , 410 - 2 . . . 410 - n may be implemented with Field-Effect Transistors (FETs).
- FETs Field-Effect Transistors
- the drains may be connected to an end of the LED array 500
- the sources may be respectively connected to the ends of the resistors 430 - 1 , 430 - 2 . . . 430 - n
- the gates may be respectively connected to the output nodes of the comparators 420 - 1 , 420 - 2 . . . 420 - n.
- the FETs may have the same size or different sizes, and may have the same allowable current or may have different allowable currents.
- the comparators 420 - 1 , 420 - 2 . . . 420 - n compare voltages of common nodes that connect to both the switching units 410 - 1 , 410 - 2 . . . 410 - n and the resistors 430 - 1 , 430 - 2 . . . 430 - n , with a preset reference voltage V REF in order to control the switching units 410 - 1 , 410 - 2 . . . 410 - n .
- the comparators 420 - 1 , 420 - 2 . . . 420 - n may be implemented with Operational Amplifiers (Op-Amps).
- the positive terminals may be connected to the reference voltage V REF
- the negative terminals may be connected to the common nodes between the resistors 430 - 1 , 430 - 2 . . . 430 - n and the switching units 410 - 1 , 410 - 2 . . . 410 - n
- the output terminals may be connected to the gates of the FETs.
- the comparators 420 - 1 , 420 - 2 . . . 420 - n receive a dimming signal.
- the comparators 420 - 1 , 420 - 2 . . . 420 - n may receive the dimming signal as an enable signal.
- the comparators 420 - 1 , 420 - 2 . . . 420 - n may respectively control the switching units 410 - 1 , 410 - 2 . . . 410 - n to supply constant currents to the LED array 500 .
- the comparators 420 - 1 , 420 - 2 . . . 420 - n may respectively control the switching units 410 - 1 , 410 - 2 . . . 410 - n to cut off the supply of the constant currents to the LED array 500 .
- the resistors 430 - 1 , 430 - 2 . . . 430 - n each respectively have an end that is connected to the switching units 410 - 1 , 410 - 2 . . . 410 - n , and another end that is grounded.
- the resistors 430 - 1 , 430 - 2 . . . 430 - n may all have the same resistance value or may each have a different resistance value.
- the LED drivers 400 - 1 , 400 - 2 . . . 400 n may supply constant currents having different amplitudes to the LED array 500 .
- a plurality of LED drivers 400 supply constant currents having an amplitude I LED to the LED array 500 .
- an allowable current of a transistor of the one constant current source is 100 mA or more. Therefore, a parasitic capacitance of the corresponding transistor increases.
- the parasitic capacitances of the transistors may be decreased.
- the LED array 500 may be driven by using a plurality of transistors each having an allowable current of about 25 mA.
- parasitic capacitances of the transistors can be lowered by using a plurality of LED drivers.
- the sizes of compensation capacitors that are used to reduce the parasitic capacitances do not need to be increased, thereby securing a fast settlement time.
- LED driver apparatus may also be realized by using two LED drivers.
- all of the plurality of LED drivers 400 supply constant currents to the LED array 500 .
- only a portion of the plurality of LED drivers 400 may be driven. For instance, such an example is described with reference to FIG. 3 .
- FIG. 3 illustrates a circuit diagram of a plurality of LED drivers according to another example that is within the scope of the present description.
- the plurality of LED drivers 400 are connected to one another in parallel and each include switching units 410 - 1 and 410 - 2 , comparators 420 - 1 and 420 - 2 , and resistors 430 - 1 and 430 - 2 .
- the switching units 410 - 1 and 410 - 2 respectively perform switching operations according to output signals of the comparators 420 - 1 and 420 - 2 .
- the switching units 410 - 1 and 410 - 2 may be implemented with FETs. If the switching units 410 - 1 and 410 - 2 are implemented with FETs, the drains may be connected to an end of the LED array 500 , the sources may be respectively connected to the ends of the resistors 430 - 1 and 430 - 2 , and the gates may be connected to the output nodes of the comparators 420 - 1 and 420 - 2 .
- the FETs may have the same size or may have different sizes.
- the comparators 420 - 1 and 420 - 2 compare voltages of common nodes that commonly connect to both the switching units 410 - 1 and 410 - 2 and the resistors 430 - 1 and 430 - 2 , with a preset reference voltage V REF in order to control the switching units 410 - 1 and 410 - 2 .
- the comparators 420 - 1 and 420 - 2 may be implemented with Op-Amps.
- the positive terminals may be connected to the reference voltage V REF
- the negative terminals may be connected to the common nodes between the resistors 430 - 1 and 430 - 2 and the switching units 410 - 1 and 410 - 2
- the output terminals may be respectively connected to gates of the FETs.
- the comparators 420 - 1 and 420 - 2 respectively receive control signals. For instance, when the comparators 420 - 1 and 420 - 2 receive the control signals of the controller 600 , the comparators 420 - 1 and 420 - 2 may respectively control the switching units 410 - 1 and 410 - 2 to supply the constant currents to the LED array 500 . In response to the control signals being turned off, the comparators 420 - 1 and 420 - 2 may respectively control the switching units 410 - 1 and 410 - 2 to cut off the supply of the constant currents to the LED array 500 .
- resistors 430 - 1 and 430 - 2 are connected to the switching units 410 - 1 and 410 - 2 , and the other ends of the resistors 430 - 1 and 430 - 2 are grounded.
- the resistors 430 - 1 and 430 - 2 may all have the same resistance value or may each have a different resistance value. In the event that the resistors 430 - 1 and 430 - 2 each have a different resistance value, the LED drivers 400 - 1 and 400 - 2 may supply constant currents having different amplitudes to the LED array 500 .
- the controller 600 controls the operation of the plurality of LED drivers 400 - 1 and 400 - 2 according to an amplitude of a constant current required for the LED array 500 .
- the controller 600 may calculate the amplitude of the constant current required for the LED array 500 according to an external control or an internal calculation and control only one of the LED drivers 400 - 1 and 400 - 2 appropriate for the calculated amplitude of the constant current to operate.
- the controller 600 may control both the two LED drivers 400 - 1 and 400 - 2 to operate.
- the controller 600 may control only the one LED driver 400 - 1 to operate.
- the controller 600 receives a dimming signal, generates the control signals according to the dimming signal, and respectively supplies the control signals to the comparators 420 - 1 and 420 - 2 .
- the controller 600 receives the input dimming signal and provides the control signals generated according to the dimming signal to the comparators 420 - 1 and 420 - 2 .
- the dimming signal and the control signals may be input into an additional AND logic circuit, and an output of the AND logic circuit may be provided as an enable signal of a comparator.
- a constant current is supplied to only one LED array.
- the LED driver apparatus may supply a plurality of constant currents to a plurality of LED arrays, respectively, by using a plurality of LED drivers.
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Abstract
Description
- This application claims the benefit under 35 U.S.C. §119(a) from Korean Patent Application No. 10-2011-0087460, filed on Aug. 30, 2011, and No. 10-2012-0053859, filed on May 21, 2012, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference for all purposes.
- 1. Field
- The following description relates to a Light Emitting Diode (LED) driver apparatus, and to, for example, an LED driver apparatus that can supply a stable constant current to an LED array by using a plurality of constant current sources.
- 2. Description of Related Art
- Liquid Crystal Displays (LCDs) are widely used because they are relatively thinner and light-weight in comparison to many other types of display apparatuses and exhibit lower driving voltage and consumes less power. However, the liquid crystal used in an LCD is a non-emitting substance that does not emit light by itself. Thus, an LCD requires an additional backlight for supplying light to its liquid crystal panel.
- A Cold Cathode Fluorescent Lamp (CCFL), a Light Emitting Diode (LED), and the like, are often used as a backlight source of an LCD. However, CCFLs use mercury and thus may cause environmental pollution. Also, CCFLs exhibit a slow response speed and a low color representation. Thus, CCFLs are inappropriate for making an LCD that is light-weight, thin, short, and/or small in size.
- LEDs do not use harmful materials such as mercury and are thus environment-friendly. In addition, LEDs allow impulse driving. Also, a light source made with LEDs exhibits a high color representation, with the ability to independently adjust the amount of light emitted from red (R), green (G), and blue (B) diodes to change the luminance, the color temperature, and the like of the obtained image. Thus, LEDs are appropriate for making an LCD that is light-weight, thin, short, and/or small in size. Therefore, LEDs have been widely used as a backlight source of LCDs and other display devices.
- In an LCD backlight unit using LEDs that are connected to one another in series, such as a backlight unit that uses LED arrays, a DC-DC converter is often used to adjust a power source supplied to the LEDs, and a driving circuit that functions as a constant current source is often used to supply a constant current to the LEDs.
- In order to maintain uniform brightness and color in a backlight, the LEDs are often driven by using the same current regardless of voltages of the LEDs. For example, a single constant current source may be provided under an LED array to supply the same constant current to the LED array.
- However, in order to supply a large constant current with an increase in a required amount of an LED current, a constant current source is typically implemented with a transistor. When a constant current source that supplies a large constant current is implemented with a transistor, a parasitic capacitance component of the transistor may become very large. This may reduce the stability of the current and/or lengthen the settlement time of the constant current. In such a current source, a large capacitance may be required to compensate for the parasitic capacitance component, and to, for instance, maintain the stability of the system. In such a case, the settlement time of the constant current source may lengthen, slowing down the time required to achieve a steady current.
- In one general aspect, there is provided a Light Emitting Diode (LED) driver apparatus including: a DC-DC converter configured to supply a driving voltage to an LED array, a plurality of LED drivers configured to drive the LED array according to a dimming signal, in which the plurality of LED drivers are connected to one another in parallel to supply currents to the LED array.
- The general aspect of LED driver apparatus may further include an input unit configured to receive the dimming signal from an external device.
- The LED drivers may be configured to supply the currents having the same amplitude to the LED array.
- The LED drivers may be configured to supply the currents having different amplitudes to the LED array.
- In the general aspect of LED driver apparatus, each of the LED drivers may include: a resistor having a first end that is grounded, a switching unit configured to selectively connect an end of the LED array to a second end of the resistor, and a comparator configured to compare a preset reference voltage with a voltage of a common node that connects to both the switching unit and the resistor.
- In the general aspect of the LED driver apparatus, the switching unit may be a Field-Effect Transistor (FET) that comprises a drain connected to an end of the LED array, a source may be connected to the common node, and a gate may be connected to an output node of the comparator.
- In the general aspect of the LED driver apparatus, the comparator may be an Operational Amplifier (Op-Amp) that is configured to receive the reference voltage through a positive terminal, to receive the voltage of the common node through a negative terminal, and to output a difference between the reference voltage and the voltage of the common node to the gate of the FET.
- The comparator may be configured to operate according to the dimming signal.
- The general aspect of the LED driver apparatus may further include: a controller configured to control an operation of the plurality of LED drivers according to an amplitude of a current required for the LED array.
- The LED array may be driven under a current having an amplitude between 50 mA and 150 mA.
- The general aspect of the LED driver apparatus may further include: a Pulse Width Modulation (PWM) signal generator configured to receive the dimming signal and generate a PWM signal, and the DC-DC converter may be configured to provide a forward bias voltage to the LED array based on the generated PWM signal.
- In another general aspect, there is provided a Liquid Crystal Display (LCD) including: a liquid crystal panel, and a backlight unit comprising an LED driver apparatus of
claim 1. - In yet another general aspect, there is provided a method of driving an LED array involving: supplying a driving voltage to an LED array using a plurality of LED drivers based on a dimming signal, in which the plurality of LED drivers receive the dimming signal from an external device, the plurality of LED drivers are connected to one another in parallel to supply currents to the LED array.
- The general aspect of the method may further involve generating a Pulse Width Modulation (PWM) signal based on the dimming signal, and supplying the PWM signal to a DC-DC converter that is configured to provide a forward bias voltage to the LED array.
- The LED drivers may be configured to supply the currents having the same amplitude to the LED array.
- The general aspect of the method may further involve: controlling an operation of the plurality of LED drivers according to an amplitude of a current required for the LED array as determined according to an external control or an internal calculation.
- In the general aspect of the method, each of the LED drivers may include: a resistor having a first end that is grounded, a switching unit configured to selectively connect an end of the LED array to a second end of the resistor, and a comparator configured to compare a preset reference voltage with a voltage of a common node that connects to both the switching unit and the resistor.
- Other features and aspects may be apparent from the following detailed description, the drawings, and the claims.
-
FIG. 1 is a diagram illustrating an example of a Light Emitting Diode (LED) driver apparatus. -
FIG. 2 is a circuit diagram illustrating examples of LED drivers. -
FIG. 3 is a circuit diagram illustrating other examples of LED drivers. - Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.
- The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the systems, apparatuses and/or methods described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness.
- Provided herein are examples of Light Emitting Diode (LED) driver apparatuses and methods of driving an LED array that are capable of supplying a stable current to an LED array and a short settlement time of the current by using a plurality of current sources.
-
FIG. 1 illustrates an example of a Light Emitting Diode (LED)driver apparatus 1000. - Referring to
FIG. 1 , theLED driver apparatus 1000 includes aninput unit 100, a Pulse Width Modulation (PWM)signal generator 200, a DC-DC converter 300, anLED driver 400, and anLED array 500. - The
input unit 100 receives a dimming signal that is used to drive theLED array 500. Examples of digital dimming methods that may be used with an LED include, but are not limited to, a direct mode, a fixed phase mode, and a phase shift mode. A direct mode refers to a method of controlling a frequency and an On-Duty signal through a Packet Assembler/Disassembler (PAD). Also, a fixed phase mode and a phase shift mode refer to methods of generating a PWM frequency in an Integrated Circuit (IC) and receiving only an On-Duty signal through a PAD to control the PWM frequency and the On-Duty signal. A dimming signal refers to a signal that is used to adjust the luminance, color temperature, and the like, of an LED or to compensate for the color temperature of the LED. In the present example, a direct mode in which the dimming signal is received from an external device is described. An external device refers to a device that is outside of theLED driver apparatus 1000. However, other modes, such as the fixed phase mode and the phase shift mode, may be used to obtain the dimming signal in other examples. - The
PWM signal generator 200 generates a PWM signal that is used to adjust a power source of theLED array 500. For instance, thePWM signal generator 200 generates the PWM signal that is used to control an amplitude of a driving voltage of the DC-DC converter 300. - The DC-
DC converter 300 includes a transistor that performs a switching operation and supplies a driving voltage to theLED array 500 according to the switching operation of the transistor. For instance, the DC-DC converter 300 may convert a DC voltage based on the PWM signal generated by thePWM signal generator 200 and may supply the converted DC voltage, such as the driving voltage, to theLED array 500. For instance, the DC-DC converter 300 may supply a voltage corresponding to a forward bias voltage of theLED array 500 to theLED array 500 so that theLED array 500 operates in a current saturation range. - A plurality of
LED drivers 400 drive theLED array 500 according to the dimming signal. For instance, theLED drivers 400 may adjust a driving current of theLED array 500 by using the dimming signal input from theinput unit 100. TheLED drivers 400 may supply the same constant current or different constant currents to theLED array 500. The structures and operations of theLED drivers 400 are further described later with reference toFIG. 2 . - The
controller 600 controls operations of theLED drivers 400 according to an amplitude of a constant current required for theLED array 500. For instance, thecontroller 600 may calculate the amplitude of the constant current required for theLED array 500 according to an external control or an internal calculation and may control all or only a portion of theLED drivers 400 that are appropriate for operating under the calculated amplitude of the constant current. - For example, in the event that each of four LED
drivers 400 may supply a constant current of a maximum of 25 mA, and a maximum amplitude of a constant current required for theLED array 500 connected to the four LED drivers is 100 mA, thecontroller 600 may control all of the fourLEDs 400 to operate. However, in the event that the maximum amplitude of the constant current required for theLED array 500 is 50 mA, thecontroller 600 may control only two LEDdrivers 400 to operate. - As described above, the
LED driver apparatus 1000 according to the present example supplies a constant current to theLED array 500 by using a plurality of LED drivers. Therefore, theLED driver apparatus 1000 may secure a stable current and a fast settlement time. -
FIG. 2 is a circuit diagram illustrating a plurality of LED drivers according to an example ofLED driver apparatus 1000. - Referring to
FIG. 2 , a plurality of LED drivers 400-1, 400-2 . . . 400-n are connected to one another in parallel and supply constant currents to theLED array 500. The constant currents supplied from the plurality ofLED drivers 400 to theLED array 500 may have the same amplitude or may have different amplitudes. Each of the plurality of LED drivers 400-1, 400-2 . . . 400-n includes switching units 410-1, 410-2 . . . 410-n, comparators 420-1, 420-2 . . . 420-n, and resistors 430-1, 430-2 . . . 430-n. - The switching units 410-1, 410-2 . . . 410-n respectively perform switching operations according to output signals of the comparators 420-1, 420-2 . . . 420-n. For example, the switching units 410-1, 410-2 . . . 410-n may be implemented with Field-Effect Transistors (FETs). In an LED driver apparatus in which the switching units 410-1, 410-2 . . . 410-n are implemented with FETs, the drains may be connected to an end of the
LED array 500, the sources may be respectively connected to the ends of the resistors 430-1, 430-2 . . . 430-n, and the gates may be respectively connected to the output nodes of the comparators 420-1, 420-2 . . . 420-n. - The FETs may have the same size or different sizes, and may have the same allowable current or may have different allowable currents.
- The comparators 420-1, 420-2 . . . 420-n compare voltages of common nodes that connect to both the switching units 410-1, 410-2 . . . 410-n and the resistors 430-1, 430-2 . . . 430-n, with a preset reference voltage VREF in order to control the switching units 410-1, 410-2 . . . 410-n. For instance, the comparators 420-1, 420-2 . . . 420-n may be implemented with Operational Amplifiers (Op-Amps). In an LED driver apparatus in which the comparators 420-1, 420-2 . . . 420-n are implemented with the Op-Amps, the positive terminals may be connected to the reference voltage VREF, the negative terminals may be connected to the common nodes between the resistors 430-1, 430-2 . . . 430-n and the switching units 410-1, 410-2 . . . 410-n, and the output terminals may be connected to the gates of the FETs.
- The comparators 420-1, 420-2 . . . 420-n receive a dimming signal. For example, the comparators 420-1, 420-2 . . . 420-n may receive the dimming signal as an enable signal. In such an LED driver apparatus, when the dimming signal is turned on, the comparators 420-1, 420-2 . . . 420-n may respectively control the switching units 410-1, 410-2 . . . 410-n to supply constant currents to the
LED array 500. Also, when the dimming signal is turned off, the comparators 420-1, 420-2 . . . 420-n may respectively control the switching units 410-1, 410-2 . . . 410-n to cut off the supply of the constant currents to theLED array 500. - The resistors 430-1, 430-2 . . . 430-n each respectively have an end that is connected to the switching units 410-1, 410-2 . . . 410-n, and another end that is grounded. The resistors 430-1, 430-2 . . . 430-n may all have the same resistance value or may each have a different resistance value. In an LED driver apparatus in which the resistors 430-1, 430-2 . . . 430-n have the different resistance values, the LED drivers 400-1, 400-2 . . . 400 n may supply constant currents having different amplitudes to the
LED array 500. - Due to the above-described circuit configuration, a plurality of
LED drivers 400 supply constant currents having an amplitude ILED to theLED array 500. In this example, the amplitude ILED is a sum of amplitudes of the constant currents of theLED drivers 400, satisfying the equation: ILED=IL1+IL2+ . . . +ILn. Since each of the constant currents of theLED drivers 400 have an amplitude of VREF/R, it follows that the amplitude ILED may be determined with the equation: ILED=VREF/R1+VREF/R2+ . . . +VREF/Rn. - In the event that the
LED array 500 requires a constant current of 100 mA, and one constant current source is used, an allowable current of a transistor of the one constant current source is 100 mA or more. Therefore, a parasitic capacitance of the corresponding transistor increases. - However, in the event that a plurality of LED drivers is used, the parasitic capacitances of the transistors may be decreased. For example, in the event that four LED drivers are used, the
LED array 500 may be driven by using a plurality of transistors each having an allowable current of about 25 mA. Thus, parasitic capacitances of the transistors can be lowered by using a plurality of LED drivers. As a result, the sizes of compensation capacitors that are used to reduce the parasitic capacitances do not need to be increased, thereby securing a fast settlement time. - It is noted that three or
more LED drivers 400 are used in the example described inFIG. 2 , but an LED driver apparatus may also be realized by using two LED drivers. Also, in the descriptions ofFIG. 2 , all of the plurality ofLED drivers 400 supply constant currents to theLED array 500. However, in other examples, only a portion of the plurality ofLED drivers 400 may be driven. For instance, such an example is described with reference toFIG. 3 . -
FIG. 3 illustrates a circuit diagram of a plurality of LED drivers according to another example that is within the scope of the present description. - Referring to
FIG. 3 , the plurality ofLED drivers 400 are connected to one another in parallel and each include switching units 410-1 and 410-2, comparators 420-1 and 420-2, and resistors 430-1 and 430-2. - The switching units 410-1 and 410-2 respectively perform switching operations according to output signals of the comparators 420-1 and 420-2. For example, the switching units 410-1 and 410-2 may be implemented with FETs. If the switching units 410-1 and 410-2 are implemented with FETs, the drains may be connected to an end of the
LED array 500, the sources may be respectively connected to the ends of the resistors 430-1 and 430-2, and the gates may be connected to the output nodes of the comparators 420-1 and 420-2. In this example, the FETs may have the same size or may have different sizes. - The comparators 420-1 and 420-2 compare voltages of common nodes that commonly connect to both the switching units 410-1 and 410-2 and the resistors 430-1 and 430-2, with a preset reference voltage VREF in order to control the switching units 410-1 and 410-2. For instance, the comparators 420-1 and 420-2 may be implemented with Op-Amps. In an LED driver apparatus in which the comparators 420-1 and 420-2 are implemented with Op-Amps, the positive terminals may be connected to the reference voltage VREF, the negative terminals may be connected to the common nodes between the resistors 430-1 and 430-2 and the switching units 410-1 and 410-2, and the output terminals may be respectively connected to gates of the FETs.
- The comparators 420-1 and 420-2 respectively receive control signals. For instance, when the comparators 420-1 and 420-2 receive the control signals of the
controller 600, the comparators 420-1 and 420-2 may respectively control the switching units 410-1 and 410-2 to supply the constant currents to theLED array 500. In response to the control signals being turned off, the comparators 420-1 and 420-2 may respectively control the switching units 410-1 and 410-2 to cut off the supply of the constant currents to theLED array 500. - One ends of the resistors 430-1 and 430-2 are connected to the switching units 410-1 and 410-2, and the other ends of the resistors 430-1 and 430-2 are grounded. The resistors 430-1 and 430-2 may all have the same resistance value or may each have a different resistance value. In the event that the resistors 430-1 and 430-2 each have a different resistance value, the LED drivers 400-1 and 400-2 may supply constant currents having different amplitudes to the
LED array 500. - The
controller 600 controls the operation of the plurality of LED drivers 400-1 and 400-2 according to an amplitude of a constant current required for theLED array 500. For instance, thecontroller 600 may calculate the amplitude of the constant current required for theLED array 500 according to an external control or an internal calculation and control only one of the LED drivers 400-1 and 400-2 appropriate for the calculated amplitude of the constant current to operate. For example, in the event that the two LED drivers 400-1 and 400-2 supply a constant current having a maximum amplitude of 25 mA, and a maxim constant current required for theconnected LED array 500 is 50 mA, thecontroller 600 may control both the two LED drivers 400-1 and 400-2 to operate. Also, provided that the maximum amplitude of the constant current required for theLED array 500 is 25 mA, thecontroller 600 may control only the one LED driver 400-1 to operate. - The
controller 600 receives a dimming signal, generates the control signals according to the dimming signal, and respectively supplies the control signals to the comparators 420-1 and 420-2. In the present example, thecontroller 600 receives the input dimming signal and provides the control signals generated according to the dimming signal to the comparators 420-1 and 420-2. However, the dimming signal and the control signals may be input into an additional AND logic circuit, and an output of the AND logic circuit may be provided as an enable signal of a comparator. - In the examples illustrated in
FIGS. 1 through 3 , a constant current is supplied to only one LED array. However, in other examples, the LED driver apparatus may supply a plurality of constant currents to a plurality of LED arrays, respectively, by using a plurality of LED drivers. - A number of examples have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.
Claims (17)
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KR1020120053859A KR101977989B1 (en) | 2011-08-30 | 2012-05-21 | Led driver apparatus |
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CN102970788A (en) | 2013-03-13 |
CN102970788B (en) | 2017-04-26 |
US9875697B2 (en) | 2018-01-23 |
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